1. Field of the Invention
The invention relates to communication system, more particularly to a error correction code decoder and receiving system.
2. Description of the Related Art
Low-density parity-check (LDPC) code is an error correction code. Since LDPC code allows data transmission rates approaching the Shannon Limit, use of the LDPC code is increasingly incorporated in communications standards such as Digital Video Broadcast-Satellite Version 2 (DVB-S2), Digital Terrestrial Multimedia Broadcasting (DTMB), and IEEE 802.11. At a receiving end, a LDPC code decoder receives (N) bits through a channel. The LDPC code decoder decodes the (N) bits, and treats each of the bits as a bit node. In order to decode correctly the (N) bits, the (N) bit nodes must satisfy (N-K) conditions, wherein the conditions are called “check node”.
To reduce channel interference, the LDPC code decoder uses the check node to verify whether the (N) bits have been received correctly. Assuming that the check nodes are zeroes, the LDPC code decoder uses the bit nodes and the check nodes to exchange iteratively probabilities of the bit nodes being ‘0’ or ‘1’, in order to restore the bits that are to be decoded. The above-described process is known as “belief propagation (BP)”.
Since iteration calculation is rather complex, the min-sum algorithm is used to approximate. Further, to prevent overestimates of probability, an offset value, namely an offset BP value, is used for correction. However, the offset value cannot change in accordance with changes in channel quality, resulting in inaccurate probabilities of the bit nodes obtained through the iterative process, and poor quality reliability indices associated with decoding output.
Although using an updated channel quality for subsequent iteration calculation was proposed in a 2006 article entitled “LDPC Decoding Algorithm with Estimation of Noise Variance” by Changzheng Ma and Boon Poh Ng, a calculation process described therein is rather complicated, and can burden hardware.